• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.10a
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• pp.483-488
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• 2002

In this paper numerical algorithm for the continuum large crack model is proposed based on the return-mapping formulation. The numerical test results show that the present algorithm works appropriately under cyclic loading. It is also shown that in continuum damage models a large crack model to prevent excessive tensile plastic strain should be used to have realistic cyclic loading simulation results.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.155-159
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• 2000

Microstructural processes during high cycle fatigue are investigated according to plastic-strain hardening, crack formation, crack propagation and fracture. It is shown that the fatigue test resembles the uniaxial tensile test. The logarithm of the number of cycles to failure is proportional to the elongation in the tensile test. Under high cycle fatigue test, the strain is normally elastic. If the strain is absolutly elastic, fatigue could not result. But this is over simplication. Nearly all metals undergo a minor amount of plastic strain even at low stress. Damage accumulation leadling to crack formation can continue in the persistent slip bands at very low average plastic strain amplitude. In the ten­s sile test the overall specimen follows the failure procedure whilst in the high cycle fatigue test the local persistent slip band follows the failure procedure. However accumulations of strain per unit volume in the deforming region before failure in both cases are equal locally.

• Journal of the Korean Society for Railway
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• v.11 no.3
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• pp.280-285
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• 2008

Two kinds of failure model, that is, the Gurson model and a shear failure model were used for the finite element analyses of simple and notch tensile specimens and axial compression of a fracture tube with initial saw-cuts. The parameter values for the shear failure model were determined by a combined experimental and numerical analysis of the notch tensile specimens. After fitting the numerical parameters such as the yielding stress and the fracture shear strains, the Gurson model and the shear failure model were applied to the analysis of the fracture tube. Although the Gurson model and the shear failure model showed similar fracture behavior for the case of the tensile specimens, the respective results were different in the axial force and the crack growth rate of the fracture tube. That is, the shear failure model required more axial force to make the cracks propagate along the tube than the Gurson model. These are believed to show the lack of damage evolution process of the shear failure model. To decide which model is better in the tube analysis, experimental verification will be necessary.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.925-928
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• 2008

Fiber is an important ingredient in strain-hardening cementitious composite (SHCC), which can control fracture of cementitious composite by bridging action. The properties of reinforcing fiber, as tensile strength, aspect ratio and elastic modulus, have great effect on the fracture behavior of SHCC. To apply SHCC to structural member, SHCC must have economical efficiency and workability as well as own excellent tensile performance. For these purposes, four-point bending and direct tensile tests on SHCC with only hybrid synthetic fibers, total fiber volume fraction, $V_f$, is 1.5%, are carried out. The research emphasis is on the mechanical properties of SHCC made in Polyvinyl alcohol (PVA) and Polyethylene (PE) fibers, and how this affects the composite property, and ultimately its strain-hardening performance. Also, effect of hybrid type and water-cement ratio on the behavior of SHCC was evaluated in this paper.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.177-180
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• 2008

SHCC shows the high energy tolerance capacity due to the interfacial bonding of the fibers to the cement matrix. For effective material design and application of SHCC, it is needed to investigate the damage process and micro-fracture mechanism of cement matrix reinforced with different types of fibers. The objective of this paper is to investigate the direct tensile response of cement composites reinforced with single and hybrid fibers using acoustic emission(AE) technique. In this study, the correlations between AE signal and result of the direct tensile response of SHCC. For these purposes, three kinds of fibers were used: PET1.5%, PET1.0+PE0.5%, PET1.0%+PVA0.5%. The result of the direct tensile response of SHCC, for the same volume fraction of fibers, ultimate strength of PET-PE specimen was 2.7 times higher than specimens with PET fibers. And from AE signal value, AE event numbers and cumulative energy were different according to kind of fiber because of the different material properties of reinforced fiber.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.3
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• pp.303-309
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• 2005

Numerical analysis is carried out to identify the appropriateness of the design codes that is available for the tensile design of fastening system at Nuclear Power Plant (NPP) in this study. This study is intended for the cast-in-place anchor that is widely used for the fastening of equipment in Korean NPPs. The microplane model and the elastic-perfectly plastic model are employed for the quasi-brittle material like concrete and for the ductile material like anchor bolt as constitutive model for numerical analysis and smeared crack model is employed to simulate the clack and damage phenomena. The developed numerical model is verified on a basis of the various test data of cast-in-place anchor. The appropriateness of both ACI 349 Code and CEB-FIP Code is evaluated for the tensile design of cast-in-place anchor and it is proved that both design codes give a conservative results for real tensile capacity of cast-in-place anchor.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.190-197
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• 2019

W-K-TiC alloys with different titanium carbide concentrations (0.05, 0.1, 0.25, 0.5, 1, 2) wt.% were fabricated through Mechanical Alloying and Spark Plasma Sintering. The effects of the addition of nano-scaled TiC particles on the relative density, Vickers micro-hardness, microstructure, crystal information, thermal shock resistance, and tensile strength were investigated. It is revealed that the doped TiC nano-particles located at the grain boundaries. The relative density and Vickers micro-hardness of W-K-TiC alloys was enhanced with TiC addition and the highest Vickers micro-hardness is 731.55. As the TiC addition increased from 0.05 to 2 wt%, the room-temperature tensile strength raised from 141 to 353 MPa. The grain size of the W-K-TiC alloys decreased sharply from $2.56{\mu}m$ to 330 nm with the enhanced TiC doping. The resistance to thermal shock damage of W-K-TiC alloys was improved slightly with the increased TiC addition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.5
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• pp.309-316
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• 2022

This paper presents nonlinear numerical analysis results which were compared with the tested tensile strengths of CFRP(Carbon Fiber Reinforced Plastic) laminates with 14 different stacking sequences. The composite laminate coupons were cured under an autoclave pressure using resin-impregnated unidirectional tapes. The nonlinearity of the matrix was considered for the analysis, which was obtained from lamina tests. The Hashin failure criteria and progressive failure analysis were used for the nonlinear finite element analysis. The comparison results show that the current approach is acceptable to predict the tensile strengths of the CFRP laminate coupons with various stacking sequences and no damage. However, it is not acceptable to predict the tensile strengths of the laminate specimens with a center hole.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.3
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• pp.245-252
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• 2012

This paper proposes a simple numerical method, based on the stress-modified fracture strain-damage model with the stress-reduction technique, for predicting the failure behaviors of ductile plates with multiple through-wall cracks. This technique is implemented using the user-defined subroutines provided in ABAQUS. For validation, the results simulated using the proposed method are compared with published experimental data of Japanese researchers.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3148-3154
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• 2010

This paper presents the probabilistic analysis for fatigue life of Glass/Epoxy laminates with impact-induced damage. For this, a series of impact tests were perfomed on the Glass/Epoxy laminates using instrumented impact testing machine. Then, tensile and fatigue tests carried out so as to generate post-impact residual strength and fatigue life. Two Parameter Weibull distribution was used to fit the residual strength and fatigue life data of Glass/Epoxy composite laminates. The residual strength was affected by impact energy and their variance decreased with increasing of impact energy. The fatigue life of impacted laminates was greatly reduced by impact energy and this trend depended on applied stress amplitude. Additionally, the variation of fatigue life was gradually decreased with the applied stress amplitude.